This invention relates to thin film magnetic heads, and in particular, to a method for fabricating narrow track width write heads comprising poles made of laminated pole-piece material.
Typical magnetic disk drives include a magnetic disk and a read-write head for recording data in and reading data from the disk. It has been a goal of industry to increase the recording density in magnetic disks. In order to achieve this goal, read-write heads have been developed comprising an inductive write element and a magnetoresistive read element. In addition, magnetic disks exhibiting high coercivity and low noise have been developed.
Advanced read-write heads with inductive write elements are expected to operate at high frequencies (e.g. greater than 10 MHz). At such frequencies, the permeability of typical head material (e.g. permalloy) tends to drop significantly, thereby leading to degraded performance. Consequently, laminated heads have been proposed to enhance high frequency permeability.
In a laminated head, the top pole is divided into two or more layers separated by thin insulation. This reduces eddy current losses, and therefore enhances high frequency performance. Lamination is discussed by Okumura, et al., "High Frequency Read/Write Characteristics for Laminated Fe--Ta--N Heads", IEEE Trans. Magnetics, Vol. 29, No. 6, November 1993, by Makino, et al., "High Density Recording FeTaN Laminated Hard Disk Heads", IEEE Trans. Magnetics, Vol. 29, No. 6, November 1993, and by Zhu, "Modeling of Lamination Effects for Thin Film Inductive Heads", 1996 Digest of Intermag '96, paper BB-04, incorporated herein by reference.
It is known in the art to use "pole-tip trimming" to reduce the write fringing field. (The fringing field is that portion of the magnetic field generated by the write element and extending toward tracks adjacent to the track being written to. See P.V. Koeppe, et al., "Effect of Pole Tip Alignment on Magnetic Fringing Fields from Recording Heads", J. Appl. Phys. 63(8), 15 Apr. 1988, pp. 4042-4044, incorporated herein by reference.) It is important to minimize the write fringing field, especially when recording in disks having a high track density (i.e., disks recorded using a narrow pole width) because otherwise, the fringing field might partially erase or garble data in adjacent tracks.
At present, ion beam etching ("IBE") is the only proven high-volume etching technique for trimming deposited pole-piece layers into poles. Use of IBE for trimming is discussed by Alan Hayes, et al., "Ion Milling for Thin-Film Head Fabrication", Data Storage, March/April 1995, incorporated herein by reference.
The use of IBE for patterned etching requires a mask to protect the portions of the read-write head that are not to be etched. The most common mask for IBE is photoresist. However, due to relatively low etch selectivity, thick photoresist is required for pole trimming. (Etch selectivity refers to the ratio of the rate at which the pole-piece material is etched to the rate at which the photoresist is etched during IBE.) This limits the efficacy of using photoresist as a mask for trimming very narrow poles (e.g. poles with an aspect ratio greater than 2.0). Further, due to thick photoresist mask requirements, "redeposition" and "shadowing" become a severe problem when trimming narrow, high aspect ratio poles. After the photoresist mask is removed, "fencings" or "rabbit ears" remain above the pole-pieces. To minimize the "fencing" problem, a complicated, long ion-milling process, e.g. using multi-angle ion milling and a tedious post-milling photoresist stripping step, is used.
It is also known in the art to use sputtered Al.sub.2 O.sub.3 as an IBE mask. During such a process, a) Al.sub.2 O.sub.3 is blanket-deposited on a workpiece to be patterned; b) photoresist is deposited on the Al.sub.2 O.sub.3 ; c) the photoresist is patterned to serve as a mask for etching the Al.sub.2 O.sub.3 ; and d) and the pattern in the photoresist is transferred to the Al.sub.2 O.sub.3 by wet etching. Unfortunately, this results in an uncontrollable "undercut" of the Al.sub.2 O.sub.3 underneath the photoresist pattern. This undercut prevents Al.sub.2 O.sub.3 from being used as a mask for trimming narrow track poles.
It is possible to pattern a carbon mask by reactive ion etching. However, carbon poorly adheres to most pole-piece materials, thus limiting its use in pole-piece trimming.